日本語

The 9EDO scale, which divides the octave into nine equal parts each of 133+1/3 cents precisely, has the peculiar property of representing certain 7-limit intervals almost exactly. A 7-limit version of 9EDO goes

1: 27/25 133.238 large limma, BP small semitone
2: 7/6 266.871 septimal minor third
3: 63/50 400.108 quasi-equal major third
4: 49/36 533.742 Arabic lute acute fourth
5: 72/49 666.258 Arabic lute grave fifth
6: 100/63 799.892 quasi-equal minor sixth
7: 12/7 933.129 septimal major sixth
8: 50/27 1066.762 grave major seventh
9: 2/1 1200.000 octave

Here the characterizations are taken from Scala, which also describes the scale itself as "Pelog Nawanada: Sunda". Chords such as 1/1 - 7/6 - 49/36 - 12/7/1 are therefore natural ones for 9EDO. The above scale generates the just intonation subgroup 2.27/25.7/3, which is closely related to 9EDO.

Notation

9edo can be notated with conventional notation, including the staff, note names, relative notation, etc. in two ways. The first preserves the melodic meaning of sharp/flat, major/minor and aug/dim, in that sharp is higher pitched than flat, and major/aug is wider than minor/dim. The disadvantage to this approach is that conventional interval arithmetic no longer works. e.g. M2 + M2 isn't M3, and D + M2 isn't E. Chord names are different because C - E - G isn't P1 - M3 - P5.

The second approach preserves the harmonic meaning of sharp/flat, major/minor and aug/dim, in that the former is always further fifthwards on the chain of fifths than the latter. Sharp is lower in pitch than flat, and major/aug is narrower than minor/dim. While this approach may seem bizarre at first, interval arithmetic and chord names work as usual. Furthermore, conventional 12edo music can be directly translated to 9edo "on the fly".

Degree	Cents	Approximate Ratios	Major wider than minor		Major narrower than minor
0	0	1/1	perfect unison	D	perfect unison	D
1	133	13/12, 12/11	minor 2nd	E	major 2nd	E
2	267	7/6	major 2nd, minor 3rd	E#, Fb	minor 2nd, major 3rd	Eb, F#
3	400	5/4, 9/7	major 3rd	F	minor 3rd	F
4	533	4/3, 11/8	perfect 4th	G	perfect 4th	G
5	667	16/11, 3/2	perfect 5th	A	perfect 5th	A
6	800	14/9, 8/5	minor 6th	B	major 6th	B
7	933	12/7	major 6th, minor 7th	B#, Cb	minor 6th, major 7th	Bb, C#
8	1067	11/6, 24/13	major 7th	C	minor 7th	C
9	1200	2/1	octave	D	octave	D

9EDO contains a pentatonic MOS scale -- 2L 3s (1 3 1 3 1) -- with a heptatonic extension -- 2L 5s (1 1 2 1 1 2 1, sometimes called "mavila" or "antidiatonic"). Indonesian pelog scales sometimes use five-tone subsets of a seven-tone superset in a similar way, and it has been suggested that Indonesian gamelan music stems from a 9EDO tradition.

9ed2-001.svg

Images

Commas

9 EDO tempers out the following commas. (Note: This assumes val < 9 14 21 25 31 33 |.)

Comma	Monzo	Value (Cents)	Name 1	Name 2	Name 3
135/128	\| -7 3 1 >	92.18	Major Chroma	Major Limma	Pelogic Comma
16875/16384	\| -14 3 4 >	51.12	Negri Comma	Double Augmentation Diesis
128/125	\| 7 0 -3 >	41.06	Diesis	Augmented Comma
2109375/2097152	\| -21 3 7 >	10.06	Semicomma	Fokker Comma
36/35	\| 2 2 -1 -1 >	48.77	Septimal Quarter Tone
525/512	\| -9 1 2 1 >	43.41	Avicenna	Avicenna's Enharmonic Diesis
49/48	\| -4 -1 0 2 >	35.70	Slendro Diesis
686/675	\| 1 -3 -2 3 >	27.99	Senga
2430/2401	\| 1 5 1 -4 >	20.79	Nuwell
1728/1715	\| 6 3 -1 -3 >	13.07	Orwellisma	Orwell Comma
225/224	\| -5 2 2 -1 >	7.71	Septimal Kleisma	Marvel Comma
6144/6125	\| 11 1 -3 -2 >	5.36	Porwell
65625/65536	\| -16 1 5 1 >	2.35	Horwell
99/98	\| -1 2 0 -2 1 >	17.58	Mothwellsma
121/120	\| -3 -1 -1 0 2 >	14.37	Biyatisma
176/175	\| 4 0 -2 -1 1 >	9.86	Valinorsma
385/384	\| -7 -1 1 1 1 >	4.50	Keenanisma
540/539	\| 2 3 1 -2 -1 >	3.21	Swetisma
91/90	\| -1 -2 -1 1 0 1 >	19.13	Superleap
676/675	\| 2 -3 -2 0 0 2 >	2.56	Parizeksma